Demand for high data rate wireless broadband transmission is increasing, with mobile data traffic expected to increase exponentially over the next decade. Carrier aggregation is a major tool to address this increased demand. Carrier aggregation is used in Long Term Evolution (LTE)-Advanced (LTE-A) systems to improve the data throughput by increasing the total bandwidth of the transmission. Carrier aggregation in LTE-A has been supported since Release 10 of the LTE-A specification (“Rel-10”) and can be used for both frequency division duplexing (FDD) and time division duplexing (TDD) systems. In FDD, the number of aggregated carriers (serving cells) can be different between downlink (DL) and uplink (UL), while for TDD, the number of carriers for both DL and UL is typically the same. The number of DL component carriers is generally greater than or the same than the number of UL carriers. The individual component carriers in DL or UL can also be of different bandwidths, with currently supported bandwidths of 1.4, 3, 5, 10, 15 and 20 MHz. In accordance with Rel-10, a maximum of five component carriers can be aggregated. However, the number of carriers that can be aggregated is expected to be further increased in Rel-13, allowing support for up to 32 component carriers.
There are different types or modes of carrier aggregation (CA). CA can aggregate contiguous component carriers within the same operating frequency band, referred to as intra-band contiguous carrier aggregation. However, due to spectrum allocation restriction, intra-band contiguous carrier aggregation may not always be possible, and non-contiguous aggregation can be used instead. Non-contiguous carrier frequency allocations can either be intra-band or inter-band, depending whether the aggregated component carriers belong to the same operating frequency band or belong to different operating frequency bands.